Optical Density (OD)
Optical density can be affected by other factors, but the mAs value becomes the factor of choice for its
control. A change in mAs of approximately 30% is required to produce a visible change in OD. As a
general rule, when only the mAs setting is changed, it should be halved or doubled. If a significant change
is not required, a repeat examination probably is not required.
When the OD of the radiograph is the only characteristic that is to be changed, the appropriate factor to
adjust would be the mAs. When the body part has been under/over penetrated or the contrast needs
adjustment, then the appropriate factor to adjust would be kVp.
1.
A radiograph is taken of the Professor McFaul’s left ankle. The resulting x-ray has too high of an
optical density (the image is too dark). She gets angry and worried about exposure. The image
was taken at 55kVp@2mAs. What should the student technologists do?
2. A patient has a radiographic image taken for her left hip. The patient is very robust and heavy in
the hip area. The resulting x-ray has a very low optical density (the image is too light). The
image was taken at 75 kVp @ 40mAs. What should the technologist do?
3. Teddy Technologist took an image of an elderly patient’s left shoulder. The resulting radiograph
had good optical density but the shoulder area was gray and washed out. Teddy wants to
improve the contrast of his image by decreasing kVp resulting in [(higher or lower) contrast?]
but keep the optical density the same. The original image was taken at 75kVp @ 15mAs. What
should Teddy do?
4.
When Sammy Supertech developed the first image of Patient Patty, the image was not
adequate. Sammy wants to improve the contrast of the Chest x-ray by widening the scale of
contrast. What factor does he need to change to widen the scale of contrast? The original xray was taken at 90kVp @ 2mAs and the OD was perfect. What technique do you think Sammy
Supertech will use for the next x-ray?
5. Kareem Abdul Jabba the Hut came into the x-ray department. He needed an x-ray of his left
knee because he twisted it in an interplanetary basketball game. As his personal technologist,
you suggest the technique of 65kVp @ 10mAs. The radiologist thinks this will result in an x-ray
that has too much OD. He would like you to change one of the factors to ensure the x-ray has
OD adequate enough to see the anatomy. Which factor(s) do you decide to decrease and why?
What is the new technique you are going to suggest?
6. Rihanna came into the x-ray department because she thinks she might have broken her left
hand when performing for a dance video. She has recently re-united with Chris Brown and
thinks she might be pregnant. You decide to pick the safest technique to image her hand. You
begin at 65kVp@ 2mAs. But your boss thinks you should shorten the scale of contrast. How
would you adjust the technique but maintain the optical density?